demo=['hello', 123, 3123]
print(len(demo))
print(demo[-1])
demo.append("world")
print(demo)
demo.pop(2)
print(demo)

L = [
    ['Apple', 'Google', 'Microsoft'],
    ['Java', 'Python', 'Ruby', 'PHP'],
    ['Adam', 'Bart', 'Bob']
]

# 打印Apple:
print(L[0][0])
# 打印Python:
print(L[1][1])
# 打印Bob:
print(L[2][3])

